High-performance gas-phase chiral enantiomer detectors based on chiral-induced spin selectivity effect

Abstract

The chirality-induced spin selectivity (CISS) effect is a state-of-art strategy for chiral detectability enhancement. For the first time, high-performance gas-phase chiral detectors based on the CISS effect were prepared using organic polymer, to address the challenges in accurately and portably detecting gas-phase chiral enantiomers in analytical chemistry. Here, a series of block copolymers poly(3-hexylthiophene)-block poly(phenyl isocyanate) (P3HT-PPI) were synthesized, combining a chiral helical structure and significantly improved electrical conductivity to regulate CISS effect by PPI ratio for precise, portable chiral recognition. P3HT₈₀-PPI₃₀ demonstrates exceptional spin polarization up to 70.8%. The gas enantiomer detector based on P3HT₈₀-PPI₃₀ exhibits excellent chiral distinguish capability of limonene enantiomers with current asymmetry factor up to 0.50, real-time detection, high reversibility, and linear concertation-dependence of response. An ‘electronic dichroism’ system based on the circuit combining chiral and achiral sensing elements, was developed for real-time visualization of limonene enantiomeric excess. Designing materials with CISS effect incorporating spin-polarized electrons in chiral enantiomer recognition and combing with conductive properties for converting chemical signals to electrical outputs, provides an effective strategy for the next-generation real-time, efficient detection of multiple chiral enantiomers.

A series of block polymers with chiral helical structures were synthesized, introducing the chiral induced spin selectivity (CISS) effect into gas-phase chiral enantiomer detection by organic polymers.

Introduction

Chiral substances are widely present in nature and play a significant role in the living organisms, recognized as the origin of life^1–3. Due to their mirror-image molecular structures, enantiomers of the same compound exhibit distinct biological activities, toxicological properties, and practical applications^4–8. Such that chiral discrimination is a persistently critical in medical research, industry safety and daily life^9,10. Traditional analytical methods, such as gas chromatography (GC) and circular dichroism (CD) spectroscopy, have been employed for chiral molecule detection and differentiation^11,12. However, these techniques require bulky instruments, substantial financial investment, and specialized operators for complex procedures, which are impractical for real-time monitoring¹³. Additionally, current research on chiral detection primarily focuses on solid/liquid phases, and detecting gas-phase enantiomers remains one of the most challenging tasks in analytical chemistry^14,15. The insufficient differentiation between enantiomers significantly impedes the advancement of gas-phase chiral discrimination. Therefore, developing portable, multifunctional detectors capable of real-time gas-phase chiral detection is crucial for rapid and convenient analysis of enantiomeric isomers across various fields, including basic research, healthcare, environmental monitoring, and industrial applications.

Chemical sensor technology offers a promising approach to achieving the goals aforementioned^16,17. In recent years, chirality sensors based on different transduction mechanisms, such as chemical resistors^18,19, optical sensors²⁰, and quartz crystal microbalances (QCMs)^21,22, have been developed for detecting gas-phase chiral analytes. These devices achieve remarkable selectivity through chiral or helical structured active layer, providing a greater response to one enantiomer than the other one by efficient Pirkle two- or three-point interactions. Photoelectron circular dichroism (PECD) and photo electron elliptical dichroism (PEELD) technology has been developed for the identification of chiral enantiomers in gas phase^23,24, but its high equipment dependency and long detection time limit its application. Compared to other chiral sensors with various output signals, the sensors based on electrical current (or resistance) as output signals offer distinct advantages in visualization and rapid detection^25,26. One of the most effective strategy currently involves using chiral molecules to functionalize inorganic conductive materials such as graphene or carbon nanotubes^27–29. This strategy can also introduce spin electrons into the molecular detection process, effectively enhancing the resolution of chiral sensors. Given the limitations inherent in material systems and working principles, achieving real-time, stable, and high-resolution detection of enantiomeric remains a significant challenge in gas-phase chiral resolution. Therefore, there is an urgent need for a novel material or detection method to prepare a new generation of gas-phase chiral detectors with high enantiomeric discrimination capability and stability.

Spin-polarized electrons can have significant effects on chemical reactions of chiral molecules and on the properties of materials which incorporate molecular chirality^30–32. The chiral-induced spin selectivity (CISS) effect is when electrons traverse or interact with helical or chiral structures, specific spin states are preferentially selected, generating spin-polarized currents^33–35. Spin currents can be produced without external magnetic fields or leads, eliminating the need for ferromagnetic materials typically required in spintronics³⁶. The CISS effect has become a hot research topic for applications in the field of non-magnetic spin-valves and room-temperature spin-light diodes^37,38. Organic molecular are characterized by long spin relaxation times up to milliseconds, are widely considered to hold immense potential for spintronic applications^39–41. Therefore, introducing the CISS effect into chiral gas-phase enantiomer detection through all-organic molecules is expected to create a new strategy for distinguish gaseous chiral molecules by utilizing spin orientation and spin propagation.

However, the poor electrical properties of existing chiral or helically structured molecules limit the generation and transport of spin-polarized electrons, resulting in the difficulty of extracting the effective electrical signals and realizing the chiral differentiation. To overcome this issue, developing block polymer that combine conductivity with chiral helical structures in the molecular chain is an expectable strategy, due to the enhancement of the generation and transport of spin-polarized electrons for sensor signal extraction and output.

In this study, we synthesized a series of chiral and conductive poly(3-hexylthiophene)-block-poly(phenyl isocyanide) (P3HT-PPI) copolymers with self-assembly helical structure for the effective discrimination of gas-phase chiral enantiomers. Efficient and stable differentiating multiple enantiomers and mixtures of chiral gas molecules is achieved by precisely adjusting the ratio of chiral and conducting units in the polymer. The assembled helical nanofiber structure significantly increases the chiroptical and electrical properties. Magnetic force atomic microscopy results indicated that the spin polarization (SP) of the assembled polymer film reached up to 70.8%, approximately twice that of the un-assembled film (SP ≈ 37%), proving that this helical structure facilitates the generation and transport of spin electrons. The device based on this assembled polymers demonstrated real-time measurement of the gas concentrations and enantiomeric compositions, realizing a discrimination factor of ≈ 0.44 for limonene gas enantiomers. Integrating the chiral and achiral detectors into the logic circuits, obtaining an ‘electronic dichroism’ (ED) system through the differential sensing performance, achieving visual quantifying enantiomers in gas mixtures.

Results

Design, preparation and performance of gas-phase chiral enantiomeric detectors

Figure 1a presents a gas-phase chiral enantiomer detector prepared based on the CISS effect. To enhance the chiral gas discrimination effect, a series of chiral and helical P3HT-PPI conductive polymers were designed (Fig. 1b). The detailed synthesis process is provided in Fig. S1 (Supplementary Information). The main chain poly (3-hexylthiophene) (P3HT) provides excellent electrical properties for the polymers. The presence of chiral source poly(phenyl isocyanide) (PPI) in the side chain disrupts the system’s spatial and inversion symmetry, enabling spin selection through chirality-induced spin-orbit coupling during electron transport (Fig. 1b (Ⅰ)). During polymer self-assembly, PPIs with unique helical structures can induce the twisting of the main chain into a helical structure, further enhancing electrical properties and electron spin selectivity (Fig. 1b (Ⅱ))^35,36. Uniform chirality and helical structure favor for a stronger interaction with one enantiomer than the other through steric effects^5,21. The ¹H NMR testing results in Fig. S2 confirm the successful synthesis of P3HT_m-PPI_n(L) (m = 80, n = 0, 10, 30, 50).

Fig. 1. Structure and electrical characterization of gas-phase enantiomer detectors.

a Schematic diagram of a gas-phase chiral enantiomer detector. b Schematic diagram of the molecular structural formulae and electron spin control in the active layer of the detector: Ⅰ) Chiral structures provide the necessary electric field symmetry breaking to modulate the electron spin orientation, Ⅱ) Chiral-induced spin selectivity effect, in which the helical nanostructures confer a preferential spin orientation for electron transport, resulting in electron spin polarization. c CD spectra of thin films of block copolymers. d−f I-V of the active layer detector of the block copolymers with different chiral source (PPI(L)) ratios in the presence and absence of chiral limonene gas. The purple curves illustrate the calculated |g_res| values. g Identification of the relative concentration of (S/R)-limonene gas used in the test by gas chromatography-mass spectrometry (GC-MS). h GC-MS testing of the gas composition, with a search of the database indicating that the gas is limonene. i Results of P3HT₈₀-PPI₃₀(D) as an active layer gas detector for different configurations of limonene gas. All tests were performed at room temperature and atmospheric pressure. Limonene concentration was constant (1,800 ppm) in all tests unless otherwise stated.

Given that the polymer’s chirality and electrical properties are essential for the detection of chiral chemical signals, these properties were systematically investigated. To induce the helical nanofiber structure, P3HT-PPI was blended self-assembled active layers with PMMA (see “Methods”). As shown in Fig. 1c, circular dichroism (CD) spectroscopy results demonstrate that as the ratio of PPI in the polymer increases, the CD signal at 258 nm gradually increases from 0 to 32 mdeg. Notably, P3HT₈₀-PPI₃₀(L) and P3HT₈₀-PPI₅₀(L) polymers exhibit additional CD absorption peaks at 300 nm compared to P3HT₈₀-PPI₁₀(L). The enhanced chiroptical properties also attributes to the increased PPI proportion, which results in a greater steric hindrance effect and promotes molecular self-assembly^42,43. The electrical performance of devices with these different ratios of PPI polymers as the active layer was tested and the device structure is shown in Fig. 1a. Due to the insulation property of PPI, the device conductivity decreases with the PPI segment increasing (Fig. S3, Supplementary Information). These results demonstrate that this P3HT-PPI polymers exhibit good chiroptical and electrical properties, favorable for chiral gas detection.

Then, these copolymers were employed as the active layer in chiral gas detectors. The current of this detector was tested as the sensing signal for distinguish vapored limonene enantiomers at concentration of 1,800 ppm (concentration is calculated by the saturated vapor pressure theory, detailed in Fig. S4, Supplementary Information). As shown in Fig. 1d–f, the current-voltage (I-V) curves of the P3HT₈₀-PPI_n devices under air condition and (S/R)-limonene exposure were measured and the current under both limonene enantiomers showed a lower value. For devices with P3HT₈₀-PPI_n(L) (n = 10, 30), the current is significantly different under the (S)-limonene and (R)-limonene exposure that the (R)-limonene gas showed lower current values than the (S)-limonene, indicating that the P3HT₈₀-PPI_n(L) exhibits a higher response to (R)-limonene gas than (S)-limonene (Fig. 1e, f). As the chiral source (PPI_n) ratio increased in the polymers, the differences between blue and red curves became more significant, indicating enhanced enantiomer discrimination capability. In contrast, for pure P3HT₈₀ devices, the curves under (S/R)-limonene overlap completely, indicating equivalent response to (S/R)-limonene gas and thus unable to differentiate chiral gases (Fig. 1d). To quantify this the chiral distinguish capability, an evaluation standard similar to circularly polarized light detection⁴⁴, defining the asymmetry factor (g_res), is applied with the calculation formula as follows:

$$g_{res}=2\times \frac{\left(R_R-R_S\right)}{\left(R_R+R_S\right)}$$ 1

Where R_R and R_S represent the device response values for the R and S configured gases, respectively. According to this equation, a larger |g_res| value indicates better chiral discrimination capability. The calculated |g_res| values are depicted by purple curves. It can be observed from Fig. 1d–f that as n in P3HT₈₀-PPI_n(L) increases from 0 to 30, the |g_res| values gradually rise to ~0.50, demonstrating excellent enantiomer discrimination. However, attempts to achieve higher |g_res| values by further increasing the n value in P3HT₈₀-PPI_n(L) proved unsuccessful, as the polymer’s poor electrical performance rendered it unsuitable for gas detection (Fig. S3). Furthermore, these two chiral gases (R/S)-limonene were characterized by gas chromatography-mass spectrometry (GC-MS) to confirm the components and concentrations of these two gases. Figure 1g shows the same peak times for both gases. The inset provides a magnified view of the chromatographic peaks, revealing similar peak intensities and areas for these two gases which validates the concentration consistency. The results of the mass spectrometry tests are shown in Fig. 1h, and the spectral library search results verify the limonene composition. This analysis confirmed that the test gases were consistent and eliminated potential response variations due to concentration differences.

To further validate the detector’s reliability in enantiomer discrimination, we also synthesized the P3HT₈₀-PPI₃₀(D) copolymer with D-configuration PPI. The P3HT₈₀-PPI₃₀(D) was fabricated into the detector, named by D-type detectors, following the same method as the P3HT₈₀-PPI₃₀(L)-based detector (named by L-type detectors). As shown in Fig. S5, P3HT₈₀-PPI₃₀(D) and P3HT₈₀-PPI₃₀(L) display mirror-symmetric CD signals. Moreover, both active layer films have virtually identical water contact angles and surface energies, suggesting consistency in the surface properties of D and L configuration-based active layer films (Fig. S6, Supplementary Information). The electrical and sensing properties measurement for the D-type detector are shown in Fig. 1i and this detector demonstrates a significantly higher response to (S)-limonene than (R)-limonene, achieving a maximum |g_res| value of around 0.36. This result is inversed with the L-type detector, demonstrating that both P3HT₈₀-PPI₃₀(D) and P3HT₈₀-PPI₃₀(L) can detect chiral limonene gases based on the steric hindrance of the opposite chiral centers of the two copolymers and the effect of currents in opposite spin directions.

Stable real-time detection of chiral gases is an essential index, which enables devices to monitor the release and accumulation of chiral species in diverse scenarios, critical for system adjustments and immediate alerts during emergencies. Considering the operating voltage, electrical performance, and chiral gas discrimination effectiveness of the detectors, P3HT₈₀-PPI₃₀(L/D) was chosen for real-time detection capability investigations at 15 V. As shown in Fig. 2a, the chiral enantiomer detector based on P3HT₈₀-PPI₃₀(L) was exposed to alternating pulses of (R/S)-limonene gas at the same concentration, with each pulse lasting 3 s, to test its dynamic response/recovery curve. When pulsed with (R)-limonene gas, the device current rapidly decreased by ~17.5 nA, indicating that the charge carriers in the active layer were effectively captured by Limonene gas, resulting in a high sensitivity of the device. In contrast, under (S)-limonene gas conditions, the device current only varied by ~11.1 nA, which is a significantly lower value. This differential response to the two chiral limonene gases is consistent with the I − V scan curve tests as aforementioned.

Fig. 2. Real-time response characteristics, concentration dependence, and mixture identification characteristics of a gas-phase enantiomer detector for (R/S)-limonene.

a Real-time response curve of the L-type detectors under (R/S)-limonene cycling pulse. b Current recovery time statistics of L-type devices in different configurations of limonene gas. c Real-time response curve of the D-type detectors under (R/S)-limonene cyclic pulses. d Response values and discrimination statistics of the L/D-type detectors for different configurations of limonene gas. e, f are the response curves of the L-type detectors as a function of (R)-limonene and (S)-limonene concentrations, respectively. g Response curve of the L-type detectors with the proportion of the (R)-limonene component in the (R/S)-limonene gas mixture (volume ratio). h Statistics of the device response values for the different gas mixtures in the graph in (g). Unless otherwise stated, V = 15 V and a pulse duration of 3 s is conducted for all real-time response curve tests.

The background effect from the N₂ flow was investigated as shown in Fig. S7 and there is barely any response to N₂, indicating that the sensing response was solely produced from (R/S)-limonene. After removing the limonene gas, the gas molecules gradually desorbed from the active layer surface and the charge carriers captured by the gas molecules relocated to a new equilibrium state, gradually restoring the device current to its initial state. Figure 2b summarizes the recovery times of the L-type detector with 16 cycles of pulsing. The average recovery times of the L-type devices under (R)- and (S)-limonene pulse conditions were only about 20.8 and 23.2 seconds, respectively. To the best of our knowledge, this is one of the shortest response and recovery times reported in the research about gas-phase chiral enantiomer detectors, and one of the very few for which real-time reversibility of gas detection has been realized (Table S1, Supplementary Information).

Reversibility tests were also performed on the D-type detector as shown in Fig. 2c. Similar to the L-type detector, the current of the D-type device rapidly decreased with the two limonene gases exposure, and the response of the D-type device to (R)-limonene (average response current (|ΔI_ave|) of about 7.8 nA) was notably lower than to (S)-limonene (|ΔI_ave| ≈ 11.1 nA). Figure 2d compares the response current variations of both L- and D-type detectors to (R/S)-limonene gas in a time-dependent response measurement, and the calculated resolution values (~0.44 and 0.35 for L- and D-type detectors, respectively) closely matched with the I-V curves. Although the asymmetry factor of the devices varies slightly due to material synthesis and self-assembly behavior, the variation remains within a reasonable range. Moreover, both L- and D-type detectors have minimal standard deviations in response current values during repeated cyclic tests (<0.23 nA), demonstrating excellent reversibility and reliability for practical application.

High-performance chiral gas detectors must simultaneously exhibit robust differentiation capabilities and linear response to chiral gas concentrations. Figure 2e and f present the dynamic test results of the L-type detector for different concentrations of (R/S)-limonene. Each gas pulse time was set at 3 s, continuously measuring the concentration dependence of the response value. As the concentration decreased from 1800 to 450 ppm, the device response, defined as |ΔI| showed a decrease from 17.6 to 3.1 nA. With the concentration increased, the device response current increased, consistent with the response measured during concentration decreasing. As shown in Fig. S8, the response current of the L-type device shows a well-fitting linear relationship with the concentration of (R)-limonene gas. The limit of detection (LOD) of the equipment reached 117.0 ppm (Fig. S9). Although the LOD of our device is higher than that of advanced analytical techniques such GC-MS, CD spectroscopy, or PEELD, which can achieve sub-ppm or even ppb-level detection limits^11,45, our helical polymer-based sensor provides a valuable trade-off between sensitivity, operational simplicity, and system-level applicability, particularly in portable or integrated chiral sensing scenarios. Similarly, the L-type detector provides reliable and stable sensing performance for (S)-limonene at various concentrations, favorable for the further electrical circuit design for this chiral sensor signal output (Fig. 2f and S10). These results validate the detector’s exceptional chiral gas sensing performance and its potential for real-world applications.

Considering the complexity of the application, it is necessary to distinguish impure enantiomers to evaluate their capability to tolerate the interference impact of chemical substances on health and the environment. Such that, we further tested these detectors for the mixtures of chiral enantiomers. Figure 2g illustrates the dynamic testing of impure limonene enantiomers using an L-type detector. The impure enantiomers were obtained by precisely controlling the mixture ratios of liquid (R)- and (S)- limonene, followed by the saturation vapor pressure method. As demonstrated in Fig. 2g, when the volume ratio of (R)-limonene in the mixed gas (exculding N₂) gradually increased from 0 to 100 v%, the device’s response current increased from 11.1−17.4 nA. Notably, as the volume ratio of (R)-limonene decreased from 100−0 v%, the device exhibited a reverse response, demonstrating excellent mixture detection capability. The response current showed a clear linear correlation with the (R)-limonene fraction (Fig. 2h), allowing for direct estimation of enantiomeric excess (ee) from the electrical signal. As demonstrated in Supplementary Fig. S11, this method enables low-cost, real-time ee analysis at relatively high gas-phase concentrations (1,800 ppm). As evidenced by the identical chromatographic peak areas in GC-MS analysis (Fig. S12), the impure enantiomers used for testing was set at the identical concentrations. Therefore, the variation in response current across different purities stems from the inherent chirality differences of the gas mixture rather than its concentration.

In more complex environments involving multicomponent gas mixtures, the prepared devices exhibit limited chiral selectivity, resulting in potential cross-interference and signal overlap among different analytes. Such overlap can obscure trace-level target signals, particularly when coexisting species or background noise are present. This limitation is common among many electrical-based gas sensors, including those using semiconductors and chemiresistive materials, which often trade high sensitivity and integration ease for molecular specificity^46,47. Despite these challenges, the detector still demonstrates significant application potential in complex environments and in medical diagnostics based on volatile biomarkers.

Explanation of device chiral enantiomer differentiation mechanism

The excellent chiral gas discrimination of detectors based on the P3HT₈₀-PPI₃₀(L/D) attributes to following factors: (ⅰ) the steric hindrance effect arising from both the chiral source and helical structure that makes the sensing layer interact differently with (R/S)-limonene^5,21,22, and (ⅱ) the helical structure with conductive properties effectively facilitates the generation and transport of spintronic electrons, substantially enhancing the CISS effect^48,49. To verify this proposed mechanism, we employed magnetic conductive atomic force microscopy (mc-AFM) to further investigate the spin polarization behavior of the P3HT-PPI active layer under environmental conditions. The electron spin selectivity impacts the reactivity of chiral molecules, aiding in the enantiomeric selectivity of interactions between chiral molecules⁵⁰. By measuring the differences in I − V curve under different magnetization directions, approximately 50 I − V curves were recorded on each sample, with the average values plotted in Fig. 3a, b. When the magnetization direction is upward, the current in P3HT₈₀-PPI₃₀(L) significantly increases with lifting the bias voltage (Fig. 3a). Conversely, with downward tip magnetization, the current remains at a smaller value. These indicate that the resistance is greater when the tip is magnetized downwards than when it is magnetized upwards. To assess how spin-selective transport influences chiral gas detection, we conducted magneto-conductance measurements in the presence of (R)- and (S)-limonene. As shown in Fig. S13a, with upward magnetization of the ferromagnetic electrode, exposure to (R)-limonene induces a larger current decay than (S)-limonene. The opposite trend is observed with downward magnetization (Fig. S13b), where (S)-limonene causes a stronger current decay than (R)-limonene. These mirror-image responses demonstrate that each enantiomer preferentially interacts with electrons of a particular spin orientation-supporting the role of spin-selective electron transport in enantiomer discrimination. Furthermore, the trend of current variation under a magnetic field is consistent with the actual sensing response current variation to (R/S)-limonene in the device. These results confirm the critical role of the CISS effect in the enantiomer discrimination process of devices.

Fig. 3. Characterization of material spin polarizability using magnetic conductive atomic force microscopy (mc-AFM).

a Room-temperature I − V curves for P3HT₈₀-PPI₃₀(L) and (b) P3HT₈₀-PPI₃₀(D), obtained using mc-AFM. Tip magnetization downwards. c Schematic of low tunnelling current for P3HT₈₀-PPI₃₀(L). d Schematic of high tunnelling current for P3HT₈₀-PPI₃₀(D). e Image of the helical structure formed by self-assembly of 0.75 mg/mL P3HT₈₀-PPI₃₀(L) polymer obtained by AFM. f Basic electrical properties and enantiomeric differentiation test against limonene for detectors obtained by blending equimolar P3HT₈₀ and PPI₃₀(L) active layers. g Basic electrical properties of detectors prepared by direct spin-coating of P3HT₈₀-PPI₃₀(L) active layers. h Statistical analysis and discrimination calculations of the response values of the L-type detector based on self-assembled P3HT₈₀-PPI₃₀(L) for gas-phase of phenylethylamine and phenylethanol.

In parallel, the magnetized tip current of P3HT₈₀-PPI₃₀(D) exhibits an opposite response compared to P3HT₈₀-PPI₃₀(L) (Fig. 3b). It is shown that the electrons are spin-polarized in the polymer and that the spin selectivity correlates with the chirality. Specifically, upward tip magnetization facilitates spin-polarized charge carriers to flow between the tip and P3HT₈₀-PPI₃₀(L). However, this flow is disrupted with downward tip magnetization, leading to increased resistance (Fig. 3c, d). The degree of spin current polarization was further evaluated via the following formula: P = [(I_up−I_down)/(I_up + I_down)] × 100%, where I_up and I_down represent the currents upward and downward of the tip magnetization, respectively. The spin polarizations of P3HT₈₀-PPI₃₀(L) and P3HT₈₀-PPI₃₀(D) were 70.8 ± 10.4% and −69.3 ± 11.3%, respectively, which are among the highest spin polarizations ratio materials reported so far. Notably, these designed block-polymers also exhibit conductivity, a rare combination of high CISS effect and electrical conductivity that holds a wide range of applications (Fig. S14 and Table S2, Supplementary Information). The SP value increases as the proportion of chiral source PPI increases, and the variation of SP values with different PPI polymerization affects their ability to distinguish the molecule chirality (Fig. S15).

The enhancement of the CISS effect and chirality discrimination capabilities was further demonstrated to correlate with the helical structure. Microstructure of self-assembled P3HT₈₀-PPI₃₀(L) films in different semiconductor concentrations prepared by stepwise dilution method indicated the presence of helical structure in the films (Fig. 3e and S16, Supplementary Information). In comparison, films with identical elemental composition to P3HT₈₀-PPI₃₀(L) prepared by blending and direct spin-coating, are non-self-assembled without helical structural (Fig. S17 and S18). Figure 3f, g illustrate the chiral discrimination tests of detectors based on active layer of blended P3HT₈₀ and PPI₃₀(L) and direct spin-coated P3HT₈₀-PPI₃₀(L). The active layer thickness was controlled through spinning parameters to match that of self-assembled P3HT₈₀-PPI₃₀(L) films (Fig. S19).

The active layer prepared by blending P3HT₈₀ and PPI₃₀(L) fails to distinguish chiral limonene gas (Fig. 3f). Due to the separation of the two components in the blended film (Fig. S17), resulting in the insulating PPI portion hindering the transfer of electrons from the P3HT region and spin orientation. In contrast, grafting PPI₃₀(L) onto the P3HT₈₀ backbone creates a homogeneous whole structure, the electrons in P3HT are more readily transported and in turn lead to the formation of spin-polarized currents under the influence of PPI₃₀(L), resulting in a certain enantiomer differentiation effect (Fig. 3g). Compared to self-assembled P3HT₈₀-PPI₃₀(L) active layer detectors, devices with non-self-assembled layers have significantly reduced chiral differentiation, electron spin polarization, and chiroptical activity (Figs. S20 and S21). These results demonstrate that molecular design and self-assembled helical structure strategies significantly enhance chiral optical signals and CISS effect of materials. In addition, we demonstrate that an individual device can efficiently discriminate between a wide range of chiral gas-phase enantiomers (Fig. 3h and S22), highlighting the versatility and generalizability of the detector platform.

Device bonding circuits for chiral gas ‘electronic dichroism’

In comparison with traditional methods of chiral molecule identification based on optics and electrochemistry, the ‘electronic dichroism’ (ED) based on sensor performance can efficiently detect chiral molecules without complex preprocessing, visualizing the chiral detection^16,51. Figure 4a shows the real-time response of P3HT₈₀-PPI₃₀(L) to various concentrations of racemic limonene. The L-type device was positively correlated with racemic limonene gas concentrations while maintaining stable electrical performance across eight consecutive tests per concentration. Figure 4b illustrates the statistical relationship between response current and gas concentration for the L-type device under (R/S)-limonene and racemic limonene pulses, revealing a strong linear correlation. The response value of the racemic gas is intermediate between the (R/S)-limonene gas response, providing a feasible condition for the subsequent implementation of ED.

Fig. 4. The enantiomers of limonene can be visualized by combining chiral devices, achiral devices, and logic circuits.

a Real-time detection of racemic limonene gas by the L-type detector. b Statistics of the response values of the L-type detector to the concentration of (R), (S), and racemic configurations of limonene and the corresponding linear fitting. c Testing of the electrical properties of the non-chiral gas detector and its responsiveness to the (R/S)-limonene gas using P3HT as the active layer. d Statistics of the response values of the non-chiral device for different Limonene. The red curve is a linear fit curve. e Current-to-voltage amplification circuit. f Indicator circuit for limonene enantiomer composition judgement. g Limonene enantiomer overdose judgement reality plot.

This implementation requires a device with concentration-dependent linear responsivity independent of molecular configuration, crucial for monitoring the gas concentration and establishing the racemic response baseline for the chiral detector. For this purpose, commercially available P3HT polymer was used to prepare the active layer of the non-chiral detector by spin-coating. Figure 4c shows that the non-chiral device using P3HT as the active layer has a good response to limonene, but has no enantiomer differentiation ability (blue and red curves overlap), with calculated asymmetry factors |g_res| remaining at 0 across different voltages. The device exhibits excellent linear response to limonene gas concentration (Fig. 4d and Fig. S23, Supplementary Information).

To visualize the automatic estimation of the composition of chiral gas in the mixtures, a system was constructed based on chiral and achiral devices combined with the circuit design, and the enantiomeric excess of limonene was characterized by the color of the lamps in the system (Fig. 4e, f). Specifically, when the system is placed in the environment to be measured, the gas concentration is determined by the response value of the achiral device, which in turn determines the corresponding racemic limonene response value of the chiral device at that concentration (black curve in Fig. 4b). Further, the circuit shown in Fig. 4e converts and amplifies this current value to establish the threshold voltage in Fig. 4f (${\text{U}}_{th}=\text{I}\times R_1\times \left(R_2+R_3\right)/R_2$). At the same time, the response current of the chiral device is converted to the input voltage in the same way. When the input voltage exceeds the threshold voltage, indicating that the chiral device’s response surpasses the racemic response at that concentration, the green LED (D1) illuminates the signal (R)-limonene excess. Conversely, (S)-limonene excess triggers the yellow LED (D2) (Fig. 4g). The dynamic demonstration process is shown in Supplementary Movie 1. Based on the good discrimination effect of chiral enantiomers provided by the spin-electron chiral detector, a concept of ED parallel to the optical technique has been constructed in combination with the circuitry, enabling real-time visual analysis of chiral molecular compositions. The ED through spin-controlled transduction will greatly promote the development of chiral detectors, and is expected to play a greater role in the field of chiral gas analysis in the future.

Discussion

In summary, a series of conducting polymers P3HT₈₀-PPI_n (n = 0, 10, 30, 50) with chiral and helical structures were designed and synthesized, achieving a high-performance chiral enantiomeric gas detector based on the CISS effect for the first time using organic polymers. As the chiral source PPI ratio increases, the chiroptical signals and chiral-induced spin-selective effects are significantly enhanced while maintaining acceptable polymer conductivity. The electron spin polarization of P3HT₈₀-PPI₃₀(L) reach to 70.8% under magnetic field-free conditions, contributing to the high-performance gaseous chiral enantiomer detectors. Driven by steric hindrance and the CISS effect, these detectors showed excellent resolving power and reversibility for a wide range of chiral gases, with asymmetric coefficients of chiral limonene response (|g_res | ) up to 0.50. The helical structure formed through polymer self-assembly enhances both electrical properties and the CISS effect. In addition, this devices show excellent linear response to limonene concentration and enantiomeric purity, which favor for constructing the ‘electronic dichroism’ (ED), by combining these devices with achiral devices and comparison circuits. This ED system enables real-time, visualized detection of the enantiomeric components of chiral limonene. This work demonstrates that conducting polymers with chiral and helical structures, featuring large steric hindrance and CISS effect, provides an effective strategy for developing high-performance chiral detectors with real-time monitoring capabilities. The resulting ED system shows promise for wide-ranging applications in preventive risk assessment, particularly in monitoring the impact of chiral molecules on human health and the environment.

Methods

Device Substrate Modification

The Si or SiO₂/Si substrate was first cleaned using a piranha solution (maintained at 180 °C for 90 min), followed by rinsing with deionized water and drying with a nitrogen flow to achieve a clean surface. Subsequently, the cleaned and dried SiO₂/Si substrate was placed in a UV-ozone cleaner for 10 min, followed by spin-coating poly(perfluoroalkenyl vinyl ether) (CYTOP) on the SiO₂/Si substrate surface at 3000 rpm for 40 s in a fume hood. Finally, the SiO₂/Si substrate modification was completed by heating at 180 °C for 15 min.

Device Fabrication

Preparation of helical polymer-based sensors

Semiconductor polymer (P3HT-PPIn) and polymethylmethacrylate (PMMA) were dissolved in 1,2-dichlorobenzene, heated at 130 °C for 2 h for full dissolution, with a semiconductor concentration of 0.75 mg mL⁻¹ and PMMA mass fraction of 3 wt%. The mixed solution was rotationally coated on the cleaned silicon substrate in a glove box at 2000 rpm for 60 s. It was then placed in a vacuum oven and dried overnight at room temperature to remove the solvent. The film on the silicon substrate was immersed in deionized water, peeled off from the silicon surface, then transferred to a SiO₂/Si substrate modified by CYTOP. The film was etched with acetone to remove the PMMA. Self-assembled helical structure of the film was achieved by PMMA co-blending. Finally, gold was thermally evaporated onto the organic layer through a mask plate to form two-terminal electrodes, where the channel length and width were kept at 4500 µm and 40 µm, respectively.

Preparation of non-helical polymer-based sensors

The semiconductor polymer was dissolved in 1,2-dichlorobenzene and heated at 130 °C for 2 h, and then the solution was directly spin-coated onto SiO₂/Si modified with CYTOP. Finally, gold electrode preparation was completed as described above to obtain the corresponding devices.

Device Characterization

The circular dichroism (CD) spectrum of the thin film was measured using a circular dichroism spectrometer (JASCO J-1500) with CYTOP-modified silica as the substrate. The morphology and thickness of the semiconductor film were characterized in tapping mode using atomic force microscopy (AFM) (Nanoscope, Veeco Instruments Inc). Electron spin polarisation was obtained by testing the I − V curves of the material films under a magnetic field using a magnetically guided atomic force microscope (AFM). Target chiral gas concentrations of 450 to 1,800 ppm were obtained by adjusting the volume ratio between the saturated vapor concentration and pure N₂ from the gas cylinder. Gas composition and relative concentrations were characterized using gas chromatography-mass spectrometry (GC-MS). The electrical and response characteristics of the detector were measured using a Keithley 4200-SCS instrument. The contact angle of water and diiodomethane on the material surface was tested using a contact angle meter (SCA20). All measurements were made at room temperature unless otherwise stated.

Author contributions

X.C.W., X.H.W., F.N. and L.Q. developed the idea and designed the experiments. L.J. synthesized the material. X.C.W., J.L. and S.W. characterized device performance and data analysis. X.C.W., X.H.W., F.N., S.W. and L.Q. co-wrote and revised the paper. All the authors discussed the results and commented on the manuscript.

Peer review

Peer review information

Nature Communications thanks Thomas Fay, Tim Schäfer and the other anonymous reviewer(s) for their contribution to the peer review of this work. A peer review file is available.

Data availability

The data that support the findings of this study are available within the paper and its Supplementary Information. Source data are provided in Supplementary Data 1. Additional data are available from the corresponding authors upon request.

Competing interests

The authors declare no competing interests.

Supplementary information

The online version contains supplementary material available at 10.1038/s41467-025-63347-9.